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Claudia ZUCCHI

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2015 - Stochastic and empirical models of the absolute asymmetric synthesis by the Soai-autocatalysis [Articolo su rivista]
Barabás, Béla; Zucchi, Claudia; Maioli, Marco; Micskei, Károly; Palyi, Gyula
abstract

Absolute asymmetric synthesis (AAS) is the preparation of pure (or excess of one) enantiomer of a chiral compound from achiral precursor(s) by a chemical reaction, without enantiopure chiral additive and/or without applied asymmetric physical field. Only one well-characterized example of AAS is known today: the Soai-autocatalysis. In an attempt at clarification of the mechanism of this particular reaction we have undertaken empirical and stochastic analysis of several parallel AAS experiments. Our results show that the initial steps of the reaction might be controlled by simple normal distribution ("coin tossing") formalism. Advanced stages of the reaction, however, appear to be of a more complicated nature. Symmetric beta distribution formalism could not be brought into correspondence with the experimental observations. A bimodal beta distribution algorithm provided suitable agreement with the experimental data. The parameters of this bimodal beta function were determined by a Polya-urn experiment (simulated by computer). Interestingly, parameters of the resulting bimodal beta function give a golden section ratio. These results show, that in this highly interesting autocatalysis two or even perhaps three catalytic cycles are cooperating. An attempt at constructing a "designed" Soai-type reaction system has also been made.

2010 - Aqueous-phase quantitative NMR determination of amino acid enantiomer ratio by (13)C-NMR using chiral neodymium shift reagent [Articolo su rivista]
FLORINI, Nicola; FAGLIONI, Francesco; ZUCCHI, Claudia; L., Caglioti; PALYI, Gyula
abstract

A neodymium-(S)-PDTA (PDTA = N,N,N',N'-tetrakis[(hydroxycarbonyl)methyl]-1,2-diaminopropane) complex was found exceptionally useful in the quantitative determination of enantiomer ratios of water-soluble natural amino acids by (13)C-NMR. The method is demonstrated on mixtures of l- and d-enantiomers of various amino acids. The interactions of the chiral shift reagent with the amino acid molecules were rationalized by molecular orbital calculations.

2008 - Evolution of chirality in consecutive asymmetric autocatalytic reaction cycles [Articolo su rivista]
Maioli, Marco; Karoly, Micskei; Zucchi, Claudia; Luciano, Caglioti; Palyi, Gyula
abstract

Closed algebraic formulae were deduced for the description of the quantitative evolution of chirality in consecutive asymmetric autocatalytic reaction cycles. These formulae enable the estimation of the initial enantiometric excesses in the very first cycles of absolute enantioselective syntheses performed by Soai-autocatalysis. The initial (statistical) excesses in the homogeneous variant of the Soai- autocatalysis show normal (Gaussian) distribution, corresponding to the "coin-tossing" model of an achiral-to-chiral transformation.

2008 - On the track of absolute enantioselective catalysis [Articolo su rivista]
L., Caglioti; B., Barabas; Faglioni, Francesco; Florini, Nicola; Lazzeretti, Paolo; Maioli, Marco; K., Micskei; K., Rabai; Taddei, Ferdinando; Zucchi, Claudia; Palyi, Gyula
abstract

The main goal of this communication is to show the utility of empirical approaches combined with mathematical methods in the research regarding the molecular basis of biological chirality. Preparative results (enantiomeric excesses, e.e.) obtained in asymmetric autocatalysis with (AAC) and without (AES) chiral additive were analyzed. Statistical calculations show, that AES (absolute enantioselective synthesis) experiments yield two independent groups of results with prevalence of the R- or S-enantiomer. These are distributed asymmetrically in a second-order beta distribution. Empirical calculations both on AAC and EAS enable to identify the very low (statistical) e. e.-s amplified by AES. These initial e. e.-s show normal distribution. Possible molecular-level reasons of these results were controlled by quantum chemical MO calculations and compatible mechanism(s) are discussed.

2007 - New Cyclosiloxanolate Cluster Complexes of Transition Metals [Articolo su rivista]
Mortalo', Cecilia; A., Caneschi; Cornia, Andrea; E., Diana; S., Faranda; V., Marvaud; M., Pizzotti; O. I., Shchegolikhina; Zucchi, Claudia; Palyi, Gyula
abstract

New cyclosiloxanolate transition metal cluster complex derivs. were prepd. PhSiO2K reacted with NiX2 (X2 = Cl2 or acac) to give K2{[η6-(PhSiO2)6]2[μ3-(OH)]2Ni4K4}, a mixed Group 1-group 10 metal complex. PhSiO2Na reacted with Ni(NH3)6I2 to give Na{[η6-(PhSiO2)6]2Ni6(μ6-I)} as the 1st example of encapsulated I- ion in siloxanolate complexes. The macrocyclic Na4{[η12-(PhSiO2)12]Cu4} complex reacted with η6-(1,3,5-C7H8)Cr(CO)3 to give the heterobimetallic adduct Na4{[η12-(PhSiO2)12]Cu4}[Cr(CO)3]3 as one of the rare examples of heterobimetallic complexes with different oxidn. nos. of the metals. The Cu deriv. {[η6-(PhSiO2)6]2Cu6(BuOH)5} reacted in MeOH/CHCl3 (1:6) with Et4NCN to give hexanuclear {[η6-(PhSiO2)6]2Cu6(η2-C3H5N2O2)2}, contg. 2-amino-2-oxoethanimidic acid Me ester monoanion ligands, product of an unexpected C-C coupling reaction. This latter complex was characterized also by x-ray diffraction crystal and mol. structure detn.

2007 - On the traces of absolute enantioselective synthesis [Relazione in Atti di Convegno]
B., Barabas; L., Caglioti; Faglioni, Francesco; Florini, Nicola; Lazzeretti, Paolo; Maioli, Marco; K., Micskei; G., Rabai; Taddei, Ferdinando; Zucchi, Claudia; Palyi, Gyula
abstract

The main goal of this communication is to show the utility of empirical approaches combined with mathematical methods in the research regarding the molecular basis of biological chirality. Preparative results (enantiomeric excesses, e.e.) obtained in asymmetric autocatalysis with (AAC) and without (AES) chiral additive were analyzed. Statistical calculations show, that AES (absolute enantioselective synthesis) experiments yield two independent groups of results with prevalence of the R- or S-enantiomer. These are distributed asymmetrically in a second-order beta distribution. Empirical calculations both on AAC and EAS enable to identify the very low (statistical) e.e.-s amplified by AES. These initial e.e.-s show normal distribution. Possible molecular-level reasons of these results were controlled by quantum chemical MO calculations and compatible mechanism(s) are discussed.

2007 - Violation of Distribution Symmetry in Statistical Evaluation of Absolute Enantioselective Synthesis [Articolo su rivista]
Bela, Barabas; Luciano, Caglioti; Zucchi, Claudia; Maioli, Marco; Karoly, Micskei; Palyi, Gyula
abstract

Enantiometric excesses obtained in absolute enantioselective synthesis by chiral autocatalysis (Soai-reaction) were statistically analyzed. Two sets of parallel experiments, which were performed under chemically different conditions, are available. The former group shows some interesting tendencies, but does not give conclusive statistical results. The sample of 84 parallel experiments, providing 39 R- and 45 S-excesses have shown that these data represent two distinct, non-symmetric sets with different non-Gaussian distributions. Clear S preference was found.

2006 - Generalization possibilities of autocatalytic absolute enantioselective synthesis [Articolo su rivista]
Micskei, K; Maioli, Marco; Zucchi, Claudia; Caglioti, L; Palyi, Gyula
abstract

A simple empirical formula enables the quantitative description of chiral autocatalysis. This formula was used for the prediction of the number of consecutive autocatalytic reaction cycles needed to obtain a high enantiomeric excess without chiral auxiliary or an asymmetric physical field (absolute enantioselective synthesis). The results show, that even less selective Soai-type systems can be used for absolute enantioselective synthesis, which, therefore, appears to be a fairly general phenomenon. (c) 2006 Published by Elsevier Ltd.

2005 - A key process of aroma evolution: fatty acid beta-oxidation in Parmesan cheese ripening [Articolo su rivista]
Bellesia, Franco; A., Pinetti; Pagnoni, Ugo Maria; Zucchi, Claudia; L., Caglioti; G., Palyi
abstract

Methylketones and short chain fatty acids constitute the main part of the compounds responsible of the aroma evolution in cheese processing, mainly during ripening. An insight into the fatty acid degradation patterns shows that a maximum enzymic activity is likely to occur up to the formation of n-hexanoic acid and 2-heptanone, which are released in higher amounts with respect to both longer and shorter chain analogues. An evolution trend of the investigated volatile organic compounds (VOCs) might be correlated to the Parmesan Cheese ageing.

2004 - Analysis of the temperature and composition dependence of viscosimetric properties of 2-butanone+2-butanol solvent mixtures [Articolo su rivista]
S., Faranda; Foca, Giorgia; Marchetti, Andrea; Tassi, Lorenzo; Ulrici, Alessandro; Zucchi, Claudia
abstract

Kinematic viscosities were measured for 2-butanone + 2-butanol binary liquid mixtures with a capillary Ubbelohde routine viscometer in the temperature range from 273.15 to 353.15 K at atmospheric pressure, and covering the whole miscibility field (0 less than or equal to x(i) less than or equal to 1). Experimental data have been correlated by means of different empirical or semiempirical relationships, such as nu = nu(T), nu = nu(x(i)), and nu = nu(T, x(i)). Viscosity deviations, Deltanu, from ideal behavior are negative at all experimental conditions, confirming that structure breaking effects prevail in the liquids. Furthermore, the thermodynamics of viscous flow and excess Gibbs energy of activation of viscous flow, G*(E), have been calculated. As an alternative and complementary approach to such investigations, the fluidity (phi) of this binary system has been analyzed by the modified-Batschinski theory. The results are discussed in terms of the specific molecular interactions between the mixture components.

2004 - Density measurements of the binary mixtures of 2-butanone and 2-butanol at temperatures from –10 to 80 °C [Articolo su rivista]
S., Faranda; Foca, Giorgia; Marchetti, Andrea; Palyi, Gyula; Tassi, Lorenzo; Zucchi, Claudia
abstract

Densities of methyl-ethyl-ketone + 2-butanol were measured at temperatures between -10 and 80 degreesC, working with the pure species and nine binary mixtures. At each experimental condition, the data were correlated by means of some empirical equations and according to well-established literature models. The estimated excess molar volumes (and some related quantities) were also evaluated by applying the Redlich-Kister equation. The results related to specific intermolecular interactions have been interpreted in terms of structural and geometrical effects.

2003 - Solvatazione selettiva di biomolecole in miscele binarie 2-butanone + 2-butanolo [Relazione in Atti di Convegno]
Foca, Giorgia; Manfredini, Matteo; Manzini, Daniela; Marchetti, Andrea; Sighinolfi, Simona; Tassi, Lorenzo; Zucchi, Claudia
abstract

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2000 - Variation of volumic properties with temperature and composition of 2-butanone+1,2 propanediol binary mixtures [Articolo su rivista]
Marchetti, Andrea; Palyi, Gyula; Tassi, Lorenzo; Ulrici, Alessandro; Zucchi, Claudia
abstract

In this work we present experimental values of the density (rho), and some related quantities such as excess molar volumes (V-E), of the 2-butanone + 1,2-propanediol binary mixtures at various temperatures in the -10 less than or equal to t / degreesC less than or equal to 80 range and as a function of mole fraction. The experimental results have been fitted to some relationships of the type rho = rho (T), rho = rho (x(i)), and rho = rho (T,x(i)) to estimate the property in correspondence of the experimental data gaps. The observed behaviour has been interpreted on the basis of specific interactions and molecular features of the components. (C) 2000 Elsevier Science B.V. All rights reserved.

1999 - Alkylcobalt Carbonyls, Part 13. Preparation and Molecular Structures of Benzyl- and Phenylacetylcobalt Carbonyls [Articolo su rivista]
Zucchi, Claudia; Cornia, Andrea; R., Boese; E., Kleinpeter; H., Alper; Palyi, Gyula
abstract

The benzyl-type Co carbonyl complexes (para-t-BuC6H4CH2)Co(CO)3PPh3 (I) and [para-ClC6H4CH2C(O)]Co(CO)3PPh3 (II) were prepd. and characterized by analyses, spectra and x-ray single-crystal diffraction. The overall structures both of the alkylcobalt-type I and the acylcobalt-type II display trigonal bipyramidal geometry, with the two noncarbonyl ligands in the two axial positions. The relevance of the stereochem. of complexes I and II to the supposed mechanism of the CO insertion/deinsertion on Co is discussed.

1998 - Bimetallic Cyclooligosiloxanolate Complexes of Copper and Nickel [Articolo su rivista]
Zucchi, Claudia; M., Mattioli; Cornia, Andrea; FABRETTI COSTANTINO, Antonio; Gavioli, Giovanna; M., Pizzotti; R., Ugo; Y. A., Pozdniakova; O. I., Shchegolikhina; A. A., Zhdanov; Palyi, Gyula
abstract

The bimetallic cyclosiloxanolate cluster complexes Na[(PhSiO2)6Cu4Ni2(μ6-Cl)(PhSiO2)6] (1) and Na[(PhSiO2)6Cu3Ni3(μ6-Cl)(PhSiO2)6] (2) were prepd. by Na+ and Ni2+ ion exchange from in situ generated Na2{[(PhSiO2)6]2Na4Ni4(OH)2}. Complexes 1 and 2 were characterized by anal., spectroscopic and electrochem. methods as well as complex 2 by single-crystal x-ray diffraction (2·7DMSO·H2O: orthorhombic, space group P212121, R = 0.076). The x-ray structure shows a sandwich-type array comprising two superimposed cyclosiloxanolate rings and an M6Cl unit in between. For the 1st time the regioselectivity of the metal ion exchange could be deduced from the x-ray structural parameters.

1998 - Heterobimetallic cyclosiloxanolate sandwich clusters: Na{[η6-cyclo(PhSiO2)6]2[Fe(OR)]2Ni4(μ6-Cl)} (R = H, Me) [Articolo su rivista]
Cornia, Andrea; FABRETTI COSTANTINO, Antonio; Gavioli, Giovanna; Zucchi, Claudia; R., Pizzotti; A., Vizi Orosz; O. I., Shchegolikhina; Y. A., Pozdniakova; Palyi, Gyula
abstract

The heterobimetallic cyclosiloxanolate sandwich clusters Na{[η6-cyclo(PhSiO2)6]2[Fe(OR)]2Ni4(μ6-Cl)} (R = H, Me) (1) were prepd. from Na2{[(PhSiO2)6]2Na4Ni4(OH)2} as solvates. The new clusters 1 were characterized by spectra (UV-visible, IR, 1H-NMR), cyclic voltammetry, cond., magnetic susceptibility, and single-crystal x-ray diffraction for 1·10MeOH (R = Me).

1997 - Electrochemical behaviour of oligometallic sandwich complexes of cyclosiloxanolate ligands [Articolo su rivista]
Borsari, Marco; Gavioli, Giovanna; Zucchi, Claudia; Palyi, Gyula; R., Psaro; R., Ugo; Oi, Shchegolikhina; Aa, Zhdanov
abstract

The conductometric and voltammetric behaviour of 16 oligocyclosiloxanolate transition metal complexes in DMF is reported and discussed. The results of the conductometric measurements indicate that in DMF most of the compounds are electrolytes and the conductivity is due prevalently to the mobile (free) Na+ cation, the contribution of the large cluster anion being negligible, The cyclic voltammetric curves show only one reversible peak couple with E-p values very close to each other. These results suggest a high extent of electronic delocalisation in the cluster core of these sandwich type complexes and permit these compounds to be regarded as heteronuclear clusters of higher-valent transition metals.

1996 - Cyclooligosiloxanolate cluster complexes of transition metals and lanthanides [Articolo su rivista]
Zucchi, Claudia; Oi, Shchegolikhina; Borsari, Marco; Cornia, Andrea; Gavioli, Giovanna; Ac, Fabretti; E., Rentschler; D., Gatteschi; R., Ugo; R., Psaro; Pozdniakova, Y. U. A.; Sv, Lindeman; A. A., Zhdanov; Palyi, Gyula
abstract

Cyclooligosiloxanolate complexes of higher valent transition metals and lanthanides were synthesized and characterized by single-crystal X-ray diffraction experiments, spectra, cyclic voltammetry, conductivity and magnetic behaviour. These complexes are sandwich-type clusters containing assemblies of 4 to 8 metals between siloxanolate ligand 'layers'. A high degree of electron delocalization in the metal containing fragment of these complexes is detected by electrochemical and magnetic measurements, The synthesis, crystal and molecular structure determined by X-ray diffraction of Na-6{[C6H5SiO2)(8)]Gd-2(4)(mu(4)-O)} is reported.

1996 - Cyclosiloxane sandwich complexes of a lanthanide metal: Na-6{[(C6H5SiO2)(8)](2)Nd-4(mu(4)-O)} [Articolo su rivista]
Oi, Shchegolikhina; Ya, Pozdniakova; Sv, Lindeman; Aa, Zhdanov; R., Psaro; R., Ugo; Gavioli, Giovanna; Battistuzzi, Raffaele; Borsari, Marco; T., Ruffer; Palyi, Gyula; Zucchi, Claudia
abstract

The oligocyclosiloxane cluster ('sandwich') complex of Nd3+, Na-6{[(C6H5SiO2)(8)]Nd-2(4)(mu(4)-O)} has been prepared and characterized by analyses, infrared spectra, single crystal X-ray diffraction, magnetic susceptibility, conductivity and cyclic voltammetry. The mu(4)-O2- anion is in a square planar coordination environment. Electrochemical studies identify the cluster core as a moiety with a delocalized electron system.

1994 - Models of rhodium complexes bound to silica: preparation, structure and interconversion of dinuclear silyloxyrhodium complexes [Articolo su rivista]
A., Viziorosz; R., Ugo; R., Psaro; A., Sironi; M., Moret; Zucchi, Claudia; Ghelfi, Franco; Palyi, Gyula
abstract

(μ-Ph3SiO)2Rh2(COD)2 (2; COD = 1,5-cyclooctadiene) and (μ2-Ph3SiO)2Rh2(CO)4 (4) were prepd. by bridging ion metathesis and interconverted by terminal ligand exchange reactions. (μ2-Me3SiO)2Rh2(COD)2 was obtained alternatively by silylation of the bridging coordinated OH groups in (μ2-OH)2Rh2(COD)2 by N,N-bis(trimethylsilyl)-trifluoroacetamide. The crystal and mol. structure of 2 and 4 (R = Ph) derivs. was detd. by x-ray diffraction. Both complexes show a double square planar roof-like structure with roof angle ω = 109.6° (2) and 126.5° (4).

1994 - REDUCTIVE COUPLING OF METHYL ALPHA-BROMO-ALPHA-CHLOROCARBOXYLATES [Articolo su rivista]
Boni, M; Ghelfi, Franco; Pagnoni, Ugo Maria; Zucchi, Claudia
abstract

CuBr-LiOCH3 in methanol efficiently promotes the reductive coupling of methyl alpha-bromo-alpha-chlorocarboxylates to dimethyl alpha,alpha'-dichloro-succinates.

1991 - Erratum: O-silylation of acylcobalt tetracarbonyls: Synthesis of a new type of dinuclear μ2-hydroxycarbene cobalt carbonyl derivatives (Journal of the Chemical Society, Chemical Communications (1991) (176)) [Articolo su rivista]
Sisak, A.; Sironi, A.; Moret, M.; Zucchi, C.; Ghelfi, F.; Palyi, G.
abstract

1991 - O-SILYLATION OF ACYLCOBALT TETRACARBONYLS - SYNTHESIS OF A NEW TYPE OF DINUCLEAR MU-2-HYDROXYCARBENE COBALT CARBONYL DERIVATIVES [Articolo su rivista]
Sisak, A; Sironi, A; Moret, M; Zucchi, Claudia; Ghelfi, Franco; Palyi, Gyula
abstract

O-Silylation of acylcobalt tetracarbonyls, RC(O)Co(CO)4, gives the dinuclear carbene complexes [{mu-2-RC(OSiR'3)}(mu-2-CO)Co2(CO)6], of which one derivative (R = Me, R' = Ph) was characterized by X-ray diffraction.